Ecole Nationale Supérieure Agronomique de Montpellier ... - CIAM

C. pruni Reimmigrants
The percentage of infected reimmigrants of C. pruni seems to remain stable during their
entire period of presence on blackthorns (table 1). Only one statistically significant difference
appeared on the 7 th May, at the end of the life period for the reimmigrants : more infected C.
pruni were detected by nested-PCR. To explain this difference, several hypotheses can be
made : 1) Some adults came from an other infected clump of P. spinosa ; 2) the reimmigrants
were mainly collected on an infected part of the hedge ; 3) the reimmigrants have had enough
time to accumulate or multiply the phytoplasma to a detectable amount. The third hypothesis
seems to be the most likely as the simple PCR detected only 1 C. pruni infected, which is
equivalent to the other periods .
C. pruni Adults of New Generation
The adults of the new generation collected during the end of May to mid-June had very
variable infection rates, from 2 to 49 %. According to the fact that the hedge is not uniformly
infected, an hypothesis could be that the collected adults were agregated either on infected or
healthy branches of P. spinosa.
From the 43 individuals detected infected by nested-PCR, only 7 were detected infected
by the simple PCR. Thus it seems that only a few individuals fly away to their overwintering
sites with a large amount of phytoplasma.
C. pruni at Overwintering Sites
No C. pruni could be found on conifers in the area of the studied blackthorn hedge
althought numerous Pinus sp are present. On the contrary, C. pruni were regularly caught on
conifers at both mountainous sites (table 2) which thus seem to be overwintering sites. At the
end of the winter, C. pruni diseappeared from conifers and could be found on P. spinosa.
From 88 C. pruni caught on conifers and tested by nested-PCR, 2 were detected infected (1
from each site). Both were also detected infected when using the simple PCR.
CONCLUSIONS
In this case study on a defined blackthorn hedge, we demonstrate : 1) that the hedge can
host infected reimmigrants during all the reproductive period of C. pruni ; 2) that it can
provide ESFY infected C. pruni in the emerging new generation ; 3) that some infected C.
pruni can be found on conifers in overwintering sites at the end of the winter (which prove
that the same insects migrate from Prunus to conifers and that the phytoplasma is retained
through all the period from July to the end of winter).
The overall observations suggest that an epidemiological cycle of ESFY can be achieved
in wild reservoirs of the phytoplasma even in the absence of Prunus orchards. On the other
hand, the blackthorn hedge do not seem to be an efficient reservoir of ESFY able to change
healthy reimmigrants landing on it into infected reimmigrants. Thus, for neighbouring
orchards, a blackthorn hedge would be more a reservoir for the vector and its natural
ennemies than a direct source of infection for the fruit trees.
LITERATURE CITED
Carraro L., Osler R., Loi N., Ermacora P., Refatti E., 1998.Transmission of european stone
fruit yellows phytoplasma by Cacopsylla pruni. Journal of Plant Pathology 80 : 233-239.
Carraro L., Loi N., Ermacora P., 2001.Transmission characteristics of the european stone fruit
yellows phytoplasma and its vector Cacopsylla pruni. European Journal of Plant
Pathology, 107 : 695-700.
Carraro L., Ferrini F., Ermacora P., Loi N., 2002. Role of wild Prunus species in the
epidemiology of European stone fruit yellows. Plant Pathology, 51 : 513-517.
Chabrolin C., 1924. Quelques maladies des arbres fruitiers de la Vallée du Rhône. Annales
des Epiphyties 10 : 265-333.
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